1. Field of the Invention
This invention relates to the structure of a Wide Voltage Operation regime Double Heterojunction Bipolar Transistor, more specifically it relates to kind of a double heterojunction bipolar transistor of a broader voltage operation Range incorporating altogether a five-period In.sub.0.49 Ga.sub.0.51 P/GaAs superlatticed confinement layer and a GaAs emitter homojunction, making possible said superlatticed confinement layer functioning as a confinement layer for a minority carrier (hole), while the base-emitter homojunction serves to control the majority carrier (electron) being emitted way from the emitter into the base, thereby achieving an elevated emitter emission efficiency and lowered compensation voltage at the same time.
2. Description of the Prior Art
Over the recent years, In.sub.0.49 Ga.sub.0.51 P/GaAs Heterojunction Bipolar Transistor, HBT, by reason of its unique high speed operation and current carrying capacities, has attained significant achievements and in the meantime brought about much attention in the field and study of microwave power as well as digital circuit application. While it is true that the In.sub.0.49 Ga.sub.0.51 P/GaAs heterojunction conduction band discontinuity, .DELTA.E.sub.C, is merely 200 mV, a blocking peak of that level can still leave its impact upon the current-voltage characteristics, and that resulting inevitably in a greater collector-emitter- offset voltage, .DELTA.V.sub.CE, and also a greater base-emitter turn-on voltage, such that quite a number of researchers, realizing that fact, followed one another in the proposing of an In.sub.0.49 Ga.sub.0.51 P/GaAs double heterojunction bipolar transistor, DHBT, with a view to resolve the problem. Since both emitter and collector are made from a same material, In.sub.0.49 Ga.sub.0.51 P, being structurally symmetrical, they may both acquire a relatively lower offset voltage. Also since the collector is basically of a larger energy gap material, compared with conventional type of heterojunction bipolar transistors, it exhibits a greater breakdown voltage, and as such is best fit for higher power applications. In addition, the wide band gap InGaP was also used to increase the collector-emitter breakdown voltage. Although, the typical magnitude of .DELTA.E.sub.C (200 mV) at InGaP/GaAs heterointerface is much smaller than that at AlGaAs/GaAs heterointerface, the .DELTA.E.sub.C still impedes the current-voltage characteristic under transistor operation. This should decrease the injection of electron from the emitter to the base especially in the small bias region and cause an undesired larger collector current saturation voltage (knee voltage). On the other hand, the electron blocking effect associated with .DELTA.E.sub.C between B-C heterojunction could cause a degraded current gain. It will also increase the collector-emitter saturation voltage, V.sub.SAT, thus decrease the effective ranging of its normal working voltages. Shortcomings as such have by and large significantly restricted the application of conventional In.sub.0.49 Ga.sub.0.51 P/GaAs heterojunction bipolar transistors in high power, high operating voltage, low power loss microwave amplification and digital circuits.
Accordingly, the afore-mentioned conventional products are still inherent with more than just one drawback, being as such, they do not qualify as the result of a good, commendable design, and need be improved somehow, the sooner the better.
In view of the many defects arising out of the structure of a conventional type double heterojunction bipolar transistor, such as those cited in the foregoing, the inventor began working for improvements sometime ago, and after years of elaborate study, has come up with a successful development of the present invention, namely, the structure of a wide voltage operation regime double heterojunction bipolar transistor